Pulse-controlled bistable multivibrator



July 20, 1954 H. s. WALLACE ET AL 2,684,440

PULSE-CONTROLLED BISTABLE MULTIVIBRATOR Filed Nov. 24. 1950 Glow 20Discharge 7711 Tube INVENTORS HENRY S. WALLACE ANDRE P TULLENERS THE/RAT TOR/V5) Patented July 20, 1954 PULSE-CGNTROLLED BISTABLEMULTIVIBRATOR Henry S. Wallace, Ariington Heights, 111., and Andre P.Tulleners, Glllett, Wis, assignors to Zenith Radio florporation, acorporation of Illinois Application November 24, 1950, Serial No.197,372

3 Claims.

This invention relates to multivibrator circuits and more particularlyto multivibrators of the single-shot or flip-flop type, that is,multivibrator circuits of the type that have two stable operatingconditions and are capable of being triggered from a first to a secondcondition by pulses of one polarity while being returned to the firstcondition by pulses of a second polarity.

The pulse-controlled bi-stable multivibrator circuit or" the inventioncomprises an electrondischarge device having a cathode, an anode, and acontrol electrode; a glow-discharge tube; a source of unidirectionaloperating potential; and a load impedance. The source of unidirectionaloperating potential and the load impedance are coupled in series withthe discharge paths of the electron-discharge device and theglow-discharge tube. The multivibrator further comprises a source ofcontrol pulses including pulse components of opposite polarities, andthe controlpulse source is coupled to the control electrode and thecathode to alternate the electron-discharge device between two differentconditions of space-current conductivity in accordance with theopposite-polarity pulse components and to render the flow-discharge tubeconductive only during intervals when the electron-discharge device ismaintained in one of these conditions. Finally, the multivibratcrcomprises an output circuit coupled to the anode and to the cathode andincluding the load impedance for developing an output signal whichvaries between two discrete potential levels in time synchronism withthe opposite-polarity control pulses.

It is, accordingly, an object of the invention to provide an improvedmultivibrator circuit having two stabl operating conditions, and whichmay be triggered from one to the other of these operating conditions bythe application of successive pulses of opposite polarities.

A further object of the invention is to provide an improvedmultivibrator circuit that is simple and expedient to construct, andwhich utilizes a minimum of component elements and associated circuitry.

The features of this invention which are believed to be new are setforth with particularity in the appended claims. The invention itself,however, together with further objects and. advantages thereof may bestbe understood by reference to the following description when taken inconjunction with the accompanying drawing, in which:

Figure 1 represents a multivibrator circuit constructed in accordancewith one embodiment of the invention;

Figure 2 shows a multivibrator circuit constructed in accordance with asecond embodiment of the invention; and,

Figure 3 shows a multivibrator constructed in accordance with apreferred embodiment of the invention.

lhe circuit of Figure 1 comprises an electrondischarge device it havinga cathode ll, an anode l2 and a control electrode [3. A glowdischargetube it is connected between the anode and cathode of device it, and maybe of the neon type or the like. Cathode H is connected to groundthrough a cathode impedance i5, and anode i2 is connected to thepositive terminal 13+ of a source of unidirectional potential through aload impedance is, the negative terminal B- or" the unidirectionalsource being connectcd to ground.

Electron-discharge device It has an input circuit comprising a pair ofinput terminals one of which is connected to ground and the other tocontrol electrode l3 through a capacitor 18, the control electrode beingconnected to ground through a grid-leak resistor it. The dischargedevice has an output circuit comprising a pair of output terminals 20connected to ground and to anode 12.

An input signal represented by curve 2! may be applied across terminalsll, this signal having positive pulse components 22 and negative pulsecomponents 23. When the multivibrator is in its first operatingcondition, device Ml is correspondingly established in a firstconductive condition and glow tube 14 is in its conductive state. Inthis first conductive condition, the space current of device it has aminimum value and may be zero. The conduction of glow tube M causescurrent to flow through load resistor l6 and through cathode resistorH5. The potential drop across resistor It establishes a predeterminedpotential level 24 in the output signal developed across terminals 20.The potential developed across cathode resistor It: applies apredetermined bias to discharge device it, maintaining this device inits first conductive condition.

The application of a positive pulse component, such as pulse 22 ofsignal 2|, to control electrode 53 increases the space current throughdevice lll, establishing the device in its second conductive condition.This increase in space current causes an additional potential dropacross load resistor 86, and the circuit parameters are so chosen thatthis additional potential drop reduces the potential applied to glowtube M to such a value that the glow tube becomes extinguished. Theextinguishment of the glow tube reduces the potential across cathoderesistor l5 suficiently to maintain device it! in its second conductivecondition until the application of a negative pulse, such as pulse 23.When device it) is in its second conductive condition, a voltage dropoccurs across load resistor 16 to establish the potential of the outputsignal at a level 25. Due to the fact that the internal impedance ofdevice If! is greater than the impedance of glow tube M (as compared intheir fully conductive states) the potential drop across resistor 16during the intervals when glow tube M is conductive exceeds that whenthe glow tube is extinguished. Therefore, the output signal may beconsidered to have positive pulse components corresponding to intervalswhen glow tube M is extinguished.

The circuit of Figure 1 is triggered, therefore, from one condition toanother by a positivepolarity pulse and is returned to its firstoperating condition by a negative-polarity pulse. Pulses of likepolarity that might occur in the input signal between the oppositepolarity pulses have no material eifect on the circuit, the circuitbeing maintained in any one operating condition until the occurrence ofa pulse having a polarity opposite to that of the pulse which triggeredthe circuit into its particular condition. Moreover, the circuit remainsin either of its operating conditions for an indefinite time and may betriggered from one to the other of these conditions solely by theapplication of opposite polarity pulses.

The multivibrator circuit of Figure 2 comprises an electron-dischargedevice 30 having a cathode M, a control electrode 32 and an anode 33.Cathode Si is connected to a point of reference potential or groundthrough a glow-discharge tube 34 which may be similar to tube M ofFigure 1; and anode 33 is connected to the positive terminal B+ of asource of unidirectional potential through a load impedance 35, thenegative terminal B- of this source being grounded.

Device 36 has an input circuit comprising a pair of input terminals 35connected to ground and to control electrode 32 through a capacitor 31.Control electrode 32 is connected to ground through a resistor 38 and tothe positive terminal of the unidirectional potential source through aresistor 39. Device 30 has an output circuit comprising output terminalsill connected to ground and to anode 33.

Assume that when the multivi-brator of Figure 2 is in its firstoperating condition, device 30 is established in a first conductivecondition in which its space current may be zero, and glow tube 34 isextinguished. During this condition,

the potential of cathode 3| approximates the potential of controlelectrode 32, the potential of the control electrode being positive withrespect to ground and being derived from the potentiometer arrangementof resistors 38, 39. Moreover, the potential drop across load resistor35 is reduced to a minimum value and the output signal has the potentialvalue 44. At this time there is an insufiicient potential applied acrossglow tube 34 to cause a discharge therein.

When a positive-polarity pulse, such as pulse as of an input signaldesignated by waveform 4!, is applied to control electrode 32, thepotential of the control electrode increases and the potential ofcathode 3i similarly increases in cathodefollower fashion until thedischarge potential of glow tube 34 is exceeded. The glow tubedischarges and provides a relatively low impedance path between cathode3i and ground. During this latter condition, the cathode bias is suchthat device is established in its second conductive condition whereinrelatively high space current flows, causing a potential drop acrossload resistor to establish the output signal at the potential level 45.The circuit is maintained in this second condition by glow tube 34 untila negative-polarity pulse is applied to control electrode 32. Theapplication of such a negative pulse reduces the space current flowingthrough device 30 and the potential across glow tube 34 to such a pointthat the glow tube becomes extinguished and the circuit returns to itsfirst operating condition.

The circuit of Figure 2 is, therefore, triggered between a first andsecond operating condition by opposite polarity pulses applied tocontrol electrode 32 of device 30, and developes an output signal acrossterminals it having negative pulse components corresponding to one ofthe operating conditions.

The preferred embodiment of the invention illustrated in Figure 3 isgenerally similar to that of Figure 2 and includes an electron-dischargedevice having a cathode 5!, a control electrode 52 and an anode 53.Cathode 5! is connected to ground through a glow-discharge tube 5 3, thedischarge tube being shunted by a compensating impedance 55. Anode 53 isconnected to the positive terminal B+ of a source of unidirectionalpotential through a load impedance 58, the negative terminal 13- of thissource being connected to ground. Control electrode 52 is connected to atap 51 on compensating impedance 55, and is also connected to anode 53through a further compensating impedance 58.

Device 50 has an input circuit Comprising a pair of input terminals 59connected to ground and to control electrode 52 through a couplingcapacitor 60; and the device has an output circuit comprising a pair ofoutput terminals 61 connected to ground and to anode 53.

The operation of the circuit of Figure 3 is essentially similar to thatof Figure 2, the positive pulse 62 of input signal 63 triggering themultivibrator from its first to its second operating condition, andnegative pulse 56 of the input signal returning the multivibrator to itsfirst operating condition. The succeeding oppositepolarity pulsecomponents of the input signal cause the multivibrator to develop acrossoutput terminals 6| an output signal 65 having negative pulse componentssuch as 66 corresponding to one of the operating conditions of themultivibrator.

It has been found that when glow-discharge tube 54 is in a conductivestate there is some tendency for the current therethrough to decreaseand the tube to return to its extinguished state. This tendency, if notcompensated, may vary the bias on cathode 5i and cause some distortionin the wave form of the negative pulse components 66 of output signal65. This characteristic of the glow-discharge tube is compensated bymeans of shunting impedance 55, tap 5! being adjusted so that anytendency for the current flow through the glow tube to decrease andalter the bias of cathode 51 results in a signal on control electrode 52of such polarity and proper amplitude that it increases the currentthrough the glow tube and opposes such tendency.

It has also been found that intermediate positive pulse components thatmight appear in the input signal succeeding component 62 yet precedingthe negative pulse 64 may have an adverse effect on the wave form of thepulse 66 of output signal 55. It is desired that such intermediatepulses have no effect whatever on the multivibrator circuit. However, itis difficult to construct a circuit wherein device 50 is fullyconductive when the multivibrator is in its second operating condition,and intermediate-positive pulse components applied to control electrode52 when the multivibrator is in this condition may increase theconduction of device 55 and cause distortions in the wave form of theoutput signal.

The effect of these intermediate pulses is compensated in the circuit ofFigure 3 by means of impedance 58 connected between anode 53 and controlelectrode 52. This last-mentioned impedance actsto reflect acompensating signal upon control electrode 52 to oppose any change inthe conduction of device 50 whenin its conductive state. However, thevalue of this impedance is made sufiiciently great so that there is nointerference with the triggering action of the circuit. Thus, should anintermediate positive pulse tend to increase the conduction of de vice59 so as to decrease the potential of anode 55, impedance 58 reflects apotential decrease to control electrode 52 to oppose such increase inthe conduction of the device. Impedances 55 and 59 have an additionalfunction of providing a desired bias potential to control electrode 52for the reason described in conjunction with Figure 2.

In one constructed embodiment of the circuit of Figure 3 the followingparameters were used, and highly satisfactory results obtained. Theseparameters are listed herein merely by way of example and are notintended to limit the invention in any way:

Resistor 55 5 megohms.

Resistor 56 68,000 ohms.

Resistor 58 7.8 megohms.

Capacitor 60 47,000 micromicrofarads.

Discharge device 50 section of a type 6SN7 tube.

Glow discharge tube Type 0B2.

54. Potential source 3+... 250 volts.

The invention provides, therefore, a highly efficient multivibratorcircuit of the single-shot or flip-flop type which may be constructedsimply and conveniently and which utilizes a minimum of component parts.

While particular embodiments of the invention have been shown anddescribed, modifications may be made, and it is intended in the appendedclaims to cover all such modifications as may fall within the truespirit and scope of the invention.

We claim:

1. A multivibrator circuit comprising: an electron-discharge devicehaving an anode, a cathode and a control electrode; a glow-dischargetube connecting said cathode to a point of reference potential; a firstcompensating impedance shunting said glow-discharge tube and having atap thereon connected to said control electrode; a second compensatingimpedance connecting said control electrode to said anode; a loadimpedance connecting said anode to a source of unidirectional potential;an input circuit coupled to said control electrode and to said point ofreference potential for applying a signal having positive and negativepulse components to said device; and an output circuit coupled to saidanode and cathode for developing an output signal having pulsecomponents determined by space current variations in saidelectron-discharge device.

2. A pulse-controlled bi-stable multivibrator circuit comprising: anelectron discharge device including a cathode, an anode, and a controlelectrode; a glow-discharge tube connecting said cathode to a point ofreference potential; a source of unidirectional operating potential; aload impedance; means coupling said source of unidirectional operatingpotential and said load impedance in series with the discharge paths ofsaid electron-discharge device and of said glowdischarge tube; a sourceof control pulses including pulse components of opposite polarities;means coupling said control-pulse source to said control electrode andto said point of reference potential to alternate saidelectron-discharge device between two different conditions of spaccurrent conductivity in accordance with said opposite-polarity pulsecomponents and to render said glow-discharge tube conductive only duringintervals when said electron-discharge device is maintained in one ofsaid conditions; and an output circuit coupled to said anode and to saidcathode and including said load impedance for developing an outputsignal which varies between two discrete potential levels in timesynchronism with said opposite-polarity control pulses.

3. A pulse-controlled lei-stable multivibrator circuit comprising: anelectron-discharge device including a cathode, an anode, and a controlelectrode; a glow-discharge tube connecting said cathode to a point ofreference potential; a source of unidirectional operating potential; aload impedance; means coupling said source of unidirectional operatingpotential and said load impedance in series with the discharge paths ofsaid electron-discharge device and of said glowdischarge tube; apotential divider extending between said source of unidirectionaloperating potential and said point of reference potential and having anintermediate point connected to said control electrode; a source ofcontrol pulses including pulse components of opposite polarities; meanscoupling said control-pulse source to said control electrode and to saidpoint of reference potential to alternate said electron-discharge devicebetween two different conditions of spacecurrent conductivity inaccordance with said opposite-polarity pulse components and to rendersaid glow-discharge tube conductive only during intervals when saidelectron-discharge device is maintained in one of said conditions; andan output circuit coupled to said anode and to said cathode andincluding said load impedance for developing an output signal whichvaries between two discrete potential levels in time synchronism withsaid opposite-polarity control pulses.

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